1. Field of the Invention
The present invention relates to an image recording apparatus, an image recording method, and a storage medium.
2. Description of the Related Art
There are known recording apparatuses which record images by repeatedly performing scanning to record by discharging ink on a recording medium, by moving a recording head in which multiple discharge orifices which discharge ink are arrayed as to unit regions of the recording medium, and sub-scanning, in which the recording medium is conveyed. This sort of recording apparatus form an image by scanning the unit region multiple times, discharging ink according to a pattern in which multiple recording pixels are laid out, corresponding to positions at which ink is to be discharged in each scan. This is known as multi-pass recording.
Recording apparatuses which record by the above-described method have been conventionally known to apply mask patterns according to various conditions. Japanese Patent Laid-Open No. 2008-229864 discloses an arrangement wherein the number of recording pixels adjacent to each other in a pattern used to perform recording in monochrome mode which readily exhibits uneven density is made to be greater than the number of recording pixels adjacent to each other in a pattern used to perform recording in color mode which readily exhibits deterioration in granularity.
On the other hand, in recent years printed products for various uses have come to be created by inkjet recording, and accordingly various types of inks and recording mediums have come to be used. Japanese Patent Laid-Open No. 1-113249 discloses a method in which an ink including resin emulsion and a water-absorption resistant recording medium. Heat is applied when the ink lands on the recording medium, causing the resin emulsion to form a film, thus fixing the color material included in the ink onto the recording medium.
However, it has been found that recording using the ink and recording medium disclosed in Japanese Patent Laid-Open No. 1-113249 may cause beading, where ink droplets come into contact with each other and attract each other. This may lead to color unevenness in the recorded image. This problem will be described in detail.
FIGS. 1A and 1B are diagrams for describing the process of recording an image by multi-pass recording, using an ink including resin emulsion and a water-absorption resistant recording medium. Description will be made here by way of an example where eight recording scans are performed to complete the image.
FIG. 1A is a schematic diagram illustrating the front surface of an image after having discharged ink by the first scan of a unit region on the recording medium. The black tiles in the grid represent the recording pixels which are the positions where ink is to be discharged to, and the circles indicated by screentone represent the state of ink droplets which have actually been discharged as to the recording pixels. FIG. 1A illustrates a case of having recorded a pattern in which the recording pixels have been dispersed so as to maximally avoid the adjacent ink droplets from coming into contact with each other.
The ink does not permeate the recording medium due to the above-described nature of the ink and recording medium. Accordingly, the ink wets and spreads on the surface of the recording medium until fixed. Even in a case of using a pattern in which the recording pixels have been maximally dispersed such as illustrated in FIG. 1A, the ink droplets may come into contact with each other on the recording medium, which may lead to the above-described beading. In a case where there are regions formed within a unit region which are low in temperature, due to variance in heating and so forth, more time is required to fix the ink, and accordingly the beading becomes more pronounced.
On the other hand, FIG. 1B is a schematic diagram illustrating the front surface of a pattern, arranged such that multiple recording pixels are adjacent, after having discharged ink by the first scan of a unit region on the recording medium. Note that the pattern illustrated in FIG. 1B includes the same number of recording pixels as the recording pixels in the pattern in FIG. 1A.
In a case where ink is discharged using the pattern illustrated in FIG. 1B, four ink droplets corresponding to the mutually adjacent four recording pixels are discharged in close proximity within the unit region, so the four ink droplets group together a form one large ink droplet. Recording using such large ink droplets provides a greater distance between the multiple large ink droplets as compared with the arrangement illustrated in FIG. 1A. Further, the four ink droplets in contact with each other form a large ink droplet by drawing close to each other. Accordingly, dots formed by the large ink droplets being fixed are smaller in diameter as compared to the state illustrated in FIG. 1B immediately after the ink has landed.
From such reasons, recording using a pattern arranged such that multiple recording pixels are adjacent enables ink to be discharged such that multiple large ink droplets are not in contact with each other, despite the number of ink droplets discharged being the same. Accordingly, beading between the multiple large ink droplets can be suppressed, and images can be recorded in which is suppressed marked color unevenness due to beading between ink droplets which have landed far away from each other.
However, it has been found that another problem occurs in images recorded using a pattern wherein multiple recording pixels are adjacent, in a case where there is recording position deviation among different scans. A case where deviation in recording medium conveyance has occurred will be described here as an example of this recording position deviation.
FIG. 2A is a schematic diagram illustrating the front surface of an image after having discharged ink according to the pattern illustrated in FIG. 1A, conveying the recording medium, and then discharging ink using a pattern in which recording pixels are dispersed in a different scan following the conveying. FIG. 2B is a schematic diagram illustrating the front surface of an image after having discharged ink according to the pattern illustrated in FIG. 1B in the first scan, conveying the recording medium, and then discharging ink using a pattern in which recording pixels are laid out adjacently in the second scan following the conveying. FIG. 3A is a schematic diagram illustrating the front surface of an image after having discharged ink according to the pattern illustrated in FIG. 1A, deviation occurs in conveyance of the recording medium, and then discharging ink using a pattern in which recording pixels are dispersed in a different scan following the conveying. FIG. 3B is a schematic diagram illustrating the front surface of an image after having discharged ink according to the pattern illustrated in FIG. 1B in the first scan, deviation occurs in conveyance of the recording medium, and then discharging ink using a pattern in which recording pixels are laid out adjacently in the second scan following the conveying. The hatched circles in FIGS. 2A through 3B represent the ink droplets discharged in the first scan, and the circles indicated by screentone represent the ink droplets discharged in the second scan.
For sake of brevity here, FIGS. 3A and 3B both illustrate a case where the conveyance amount has deviated just one pixel to the upstream side in the Y direction. Accordingly, a comparison of FIGS. 2A and 2B with FIGS. 3A and 3B reveals that ink droplets are discharged at positions deviated one pixel worth to the upstream side in the Y direction as compared to the respective recording pixels in the case of conveyance deviation illustrated in FIGS. 3A and 3B.
In a case of using the pattern where the recording pixels are dispersed, occurrence of conveyance deviation changes the ink droplet coverage area little as compared to the case without conveyance deviation illustrated in FIG. 2A, as can be seen from FIG. 3A.
On the other hand, in a case of using the pattern where the recording pixels are laid out adjacently, occurrence of conveyance deviation markedly reduces the ink droplet coverage area as compared to the case without conveyance deviation illustrated in FIG. 2B, as can be seen from FIG. 3B. Accordingly, multiple regions 100 to which no ink has been discharged (hereinafter also referred to as non-discharge region) are formed extending several pixels worth in the X direction. Such non-discharge regions 100 allow the front surface of the recording medium to show through in the final image, which is visually recognized as white spots. Thus, non-discharge regions 100 are an image quality deteriorating factor.
Also, in a case where the first scan and the second scan are far away from each other (e.g., in a case of an apparatus which records with eight scans, where the first scan is scan No. 1 and the second scan is scan No. 5), the greater the chance is that the above-described conveyance deviation will occur, so white spots occur more readily.
While description has been made here regarding a case where non-discharge regions occur at the time of conveyance deviation of the recording medium, non-discharge regions occur due to various types of recording position deviation when using the pattern where multiple recording pixels are laid out adjacently, as described above. For example, the above-described non-discharge regions occur more readily when using a so-called joint head, where multiple discharge orifice rows of multiple discharge orifice rows corresponding to the same color ink arrayed in the Y direction, are arrayed in the Y direction.
FIGS. 4A and 4B are diagrams for describing the mechanism of non-discharge regions being formed in a case of using a joint head. FIG. 4A is a diagram illustrating a joint head configured with multiple discharge orifice rows having been disposed without error. Consideration will now be made regarding a case of performing recording by two scans of a unit region on the recording medium, to record by multi-path recording using such a joint head 123a. In this case, at the first scan ink is discharged from a discharge orifice row 122a, the unit region is conveyed from position 123 to position 124, and at the second scan ink is discharged from discharge orifice row 122b, thereby recording the image.
However, there are cases where the discharge orifice row 122b is disposed rotated from the proper position illustrated in FIG. 4A, due to manufacturing error at the time of manufacturing the joint head, as illustrated in FIG. 4B. Performing recording by the above-described multi-pass method using such a joint head 123b results in the discharge positions of ink deviating on both the X direction and Y direction when discharging ink from the discharge orifice row 122b. Accordingly, ink is not discharged to the portion of the recording medium corresponding to a region 126 of the joint head 123b illustrated in FIG. 4B, resulting in the above-described non-discharge region of ink.